Current, tension, power and resistance are connected among themselves by certain ratios. Any of these four sizes can be calculated if two others are known at least. At three known other sizes the information becomes redundant.
Instruction
1. Before implementation of any calculations surely transfer all data which are available in a statement of the problem to the SI system. Tension has to be expressed in volts, current - in amperes, resistance - in ohms, power - in watts. Most often concerning these sizes prefixes "micro" (one million, for short - mk), "miles" (one thousand, for short - m), by "kilogram" (one thousand, for short - j), "mega" (one million, for short - M) and "gigabyte" are used (one billion, for short-).
2. To find current at the known tension and resistance, use the law of Ohm for an incomplete chain, having carried out calculation on such formula: I=U/R, where I - current, U - tension, R - resistance.
3. If the power and resistance are known, use the following ratio: U=RI, P=UI, therefore, P=R(I^2) From here, I^2=P/R, so, I=sqrt(P/R), where I - current, P - the power, R - resistance.
4. At the known tension and power of calculation you see off so: P=UI, therefore, I=P/U, where I - current, P - the power, U - tension.
5. After calculations are ended, transfer result from the SI system to those units in which it is required to be expressed under the terms of a task (most often it is milliamperes or microamperes).
6. In case calculations are carried out in the report to laboratory work, them if necessary check result on real laboratory installation, it is simple to change tension and current, respectively, the voltmeter and the ampermeter. If at the same time high tension is used, you perform measurements with care. Measure resistance by an ohmmeter at powered off installation. As for the thermal power allocated on loading, it is not so simple to measure it as the calorimeter is required.
7. If you study in high school or in a higher educational institution, the teacher can demand from you at execution of the solution of a task to calculate an error of measurement and calculation in the standard way.